The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
(1) Field of the Invention
The present invention relates generally to antennas. More particularly, this invention relates to an antenna in a buoy towed behind a submarine for communications with satellites.
(2) Description of the Prior Art
Communications between submersibles such as submarines and remote stations are in a continuous state of development to assure the reliable exchange of information. Transmitting messages acoustically often is not acceptable since this mode of transmission may introduce the problems associated with large systems operating in low ranges and covertness can be compromised at these and higher acoustic frequencies.
Bi-directional electromagnetic transmissions have been used with some success, but usually an antenna must extend through the water-air interface for successful operation. Unfortunately, the upwardly extending antennas can be detected by radar, visual and other means, to possibly reveal the presence of the submarine. Some antennas have been made to float on the surface of the water but still their size tends to make them detectable, and they are hard to deploy, retrieve, and stow from the limited spaces for stowage on submarines. In addition most, if not all of the antennas have non-uniform, or lobed radiation and detection patterns so that the submarine platform may miss or not complete some transmissions. This could require the submarine to change its course to reorient the antenna for desired transmission/reception qualities.
U.S. Pat. No. 5,517,202 to Jayant S. Patel et al. discloses a buoyant antenna-tow body structure that has an elongate cylindrical shell having a number of aligned sensor or antenna elements inside of it. The ""202 structure may be relatively long and may create problems during stowage, launch, and retrieval on a submarine. The tow body structure of U.S. Pat. No. 5,406,903 could be used as an antenna carrier structure, and has shown a righting capability that is favorable for successful operation. However, neither of these discloses an arrangement supporting an antenna having an entire 180xc2x0 hemispherical pattern. One antenna that may be used in the ""202 or ""903 structures has been developed for operation at the surface of the water and is shown in U.S. Pat. No. 6,127,983 to David Rivera et al. The antenna has an elongate metal cylinder having an longitudinal slot that may be encapsulated in a tow body and towed at the surface of the water, however; the ""983 antenna is somewhat large and does not have a complete 180xc2x0 hemispherical, omni-directional transmission and reception pattern. Furthermore, while the ""983 antenna may function satisfactorily in same directions, it has pattern nulls i.e., is blind, in the fore and aft directions.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a low-profile broadband, omni-directional antenna that may be towed by a submarine at the water/air interface to assure reliable communications over a 180xc2x0 hemispherical pattern.
The first object of the invention is to provide a low profile antenna towed at the water/air interface by a submarine.
Another object is to provide a low-profile antenna towed by a submarine to provide for different broadband communications.
Another object is to provide a low-profile antenna towed at the surface of the water having a 180xc2x0 hemispherical radiation/detection pattern of electromagnetic signals in the air.
Another object is to provide a cost-effective antenna of reduced size, complexity and weight to allow for stowage on, deployment from, and retrieval to a submarine.
Another object is to provide a plurality of reliable antennas at the water/air interface each being optionally tunable to one or different bandwidths for selective coverage for a submarine.
Another object of the invention provides a low profile antenna to assure reliable omni-directional communication of electromagnetic signals over a virtual 180xc2x0 hemispherical pattern.
These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims.
Accordingly, the present invention is an antenna for wide bandwidth transmission and reception of electromagnetic energy signals. The antenna has an elongate semi-cylindrical shell, and a circular end disc is connected to one end, and a semi-circular end disc connected to the other end to form a half-cylinder cavity. A curved plate is connected to the circular end disc and has a curved body portion and a curved end extending parallel with the semi-cylindrical shell. A vertical stem has an upper portion connected to the curved plate. The semi-cylindrical shell, circular end disc, semi-circular end disc, and vertical stem are made from a material that is conductive of electromagnetic signals, and they can be differently dimensioned to change the center frequencies to different broadband ranges.